System and method for handling bulk materials

ABSTRACT

A bulk material handling system generally consisting of means for holding the material; means for conveying the material including a first conduit formed of a permeable material having an inlet communicating with an outlet of the material holding means and an outlet, a second conduit formed of an impermeable material encompassing and spaced from the first conduit, providing a chamber therebetween, and an auger disposed in the first conduit for transporting material received through the inlet to the outlet thereof; means for rotatably driving the auger; and means for supplying a fluidizing gas under pressure to the chamber between the first and second conduits.

This application is a divisional application of U.S. patent applicationSer. No. 11/320,572 filed on Dec. 30, 2005 now U.S. Pat. No. 7,137,759.

This invention relates to an improved system and method for handlingbulk materials, and more particularly to an improved system and methodfor conveying metered amounts of such materials having poor flowability.The invention further contemplates a novel apparatus for conveying suchmaterials.

BACKGROUND OF THE INVENTION

In a number of industries involved in the handling of bulk materialshaving poor flow characteristics, it commonly has been the practice toconvey such materials by means of mechanical conveyors. Typically, suchconveyors have consisted of screw conveyors, generally comprising anelongated, rotatable auger housed in an elongated tube. In the use ofsuch conveyors, however, it has been found that the flow rates ofsluggish and cohesive bulk materials is poor, the flow rates of suchmaterials are difficult to control, a substantial amount of torque isrequired to operate such conveyors and such materials tend to build upin the tube around the auger which often is difficult, time consumingand cumbersome to clean. In addition, because of a lack of control ofthe flow rates in such conveyors, it is difficult to accurately metersuch materials as often is required in various processes. Accordingly,it is the principal object of the present invention to provide animproved system and method for conveying bulk materials having poor flowcharacteristic with the use of a screw type conveyor in which the flowrate of sluggish and cohesive bulk materials is improved, the torquerequired to drive the augers of such conveyors is reduced and a buildupin the conduit surrounding the auger of such conveyors is reduced if notentirely eliminated.

SUMMARY OF THE INVENTION

The principal object of the present invention is achieved by providing abulk material handling system generally consisting of means for holdinga supply of such material; means for conveying the material including afirst conduit formed of a permeable material having an inletcommunicating with an outlet of a material holding means and an outlet,a second conduit formed of a impermeable material encompassing andspaced from the permeable conduit, providing a chamber therebetween, andan auger disposed in the permeable conduit for transporting materialreceived through the inlet to the outlet thereof; means for rotatablydriving the auger; and means for supplying a fluidizing gas underpressure to the chamber whereby such fluidizing gas penetrates the innerpermeable conduit encasing the auger, which forms a boundary layerconsisting of a mixture of fluidizing gas and particles of the bulkmaterial being conveyed, thus reducing surface friction andcorrespondingly enhancing the flow of material propelled by the auger.In such an arrangement, the flow rate may be more readily controlled bysimply controlling the speed of the drive motor for the auger. Moreaccurate amounts of material may be metered simply by monitoring thefeed rate of material being discharged from the screw conveyor,comparing such feed rate with a selected feed rate and correspondinglyadjusting such feed rate by controlling the speed of the drive motor forthe screw conveyor; monitoring the loss of weight of material fed intothe screw conveyor; comparing such loss of weight with a selected weightand adjusting the speed and/or discontinuing the operation of the drivemotor; and monitoring a gain of weight of material discharged from suchscrew conveyor, comparing such weight to a predetermined weight andcorrespondingly adjusting the speed and/or discontinuing the operationof the drive motor. The supply of fluidizing air to the inner conduit ofthe screw conveyor surrounding the auger functions not only to improvethe flow rate of sluggish and cohesive materials through the screwconveyor but reduces the amount of torque required to drive the auger ofthe conveyor, permits more precise control of the flow rate and preventsthe buildup of material in the conveyor requiring periodic cleaning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a first embodiment of the presentinvention;

FIG. 2 is an enlarged, perspective view of the drive motor of the screwconveyor shown in FIG. 1, having portions thereof broken away;

FIG. 3 is an enlarged view of the screw conveyor shown in FIG. 1, havinga portion thereof broken away;

FIG. 4 is a cross sectional view taken along line 4-4 in FIG. 3;

FIG. 5 is an enlarged front view of a mating flange utilized in thescrew conveyor shown in FIG. 3;

FIG. 6 is a sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is a diagrammatic-schematic view of another embodiment of theinvention;

FIG. 8 is a front view of a control panel used with the embodiment shownin FIG. 7;

FIG. 9 is a diagrammatic-schematic view of a third embodiment of theinvention; and

FIG. 10 is a diagrammatic-schematic view of a fourth embodiment of theinvention.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1 through 6 of the drawings, there is illustrated asystem for conveying a bulk material generally consisting of a hopper 20for holding a supply of bulk material to be conveyed, a receptacle 21 towhich material from the hopper is to be conveyed and a screw conveyor 22operatively interconnecting the hopper and the receptacle for conveyingmaterial from the hopper to the receptacle. Hopper 20 includes an upper,cylindrical section 22 supported on a frame structure 23 and a lower,inverted frusto-concially configured section 24. The upper end of hoppersection 22 is open to receive the lower end of a bag 25 having a set ofstraps at an upper end thereof for suspending the bag from the upper endof the frame structure, and a lower outlet spout through which bulkmaterial contained in the bag may flow into the hopper. The lower end ofhopper section 24 is provided with a mating flange 26 for connecting theoutlet of the hopper to an inlet of the screw conveyor. Typically, thehopper functions to permit the gravity flow of material received fromthe bulk bag through the hopper and the outlet thereof. Preferably, thelower section of the hopper is provided with a boundary layer offluidize gas, usually air, to enhance the gravity flow of materialthrough the lower hopper section. Receptacle 21 may consist of any formof receptacle for receiving material from screw conveyor 22. It mayconsist of a conduit for guiding material to a processing piece ofequipment, a storage container, a transportable container or any othertype of apparatus. The upper end thereof is provided with a matingflange 27 for connecting the discharge end of the screw conveyor toreceptacle 21.

Screw conveyor 22 generally includes a transport line 30 housing anauger 31, a transition section 32 interconnecting and intercommunicatingthe lower hopper section and an inlet end of transport line 30, atransition section 33 interconnecting and intercommunicating an outletend of transport line 30 and receptacle 21 and a motor unit 34 mountedon section 32 and operatively connected to auger 31.

Transport line 30 consists of an inner, tubular conduit 40 defining amaterial passageway 41 in which auger 31 is axially disposed, a pair ofannular mating flanges 42 and 43 and an outer, tubular conduit 44 spacedfrom conduit 40 and disposed between annular flanges 42 and 43 toprovide an annular chamber 45 provided with a pair of inlets 46 and 47.Inner conduit 40 is formed of a gas permeable material and outer conduit44 is formed of a gas impermeable material so that when inlets 46 and 47are connected to a source of gas under pressure, a supply of fluidizinggas will be introduced into chamber 45 and permeate through innerconduit 40 to form a boundary layer within passageway 41 consisting of amixture of fluidizing gas and particles of bulk material transportedthrough passageway 41. Although a single, linear transition line sectionis illustrated, it is to be understood that a plurality of such sectionsmay be utilized to provide transport lines of various lengths.

Transition sections 32 and 33 are substantially similar in constructionand function. Transition section 32 is adapted to be connected to anupstream end of transport line section 30 and includes a first segment50 and a second segment 51. Segment 50 includes an inner, tubularconduit 52 having the same diameter as conduit 40 and disposed in axialalignment therewith to define a passageway 53 communicating withpassageway 41, a mating flange 54 mating with and connected preferablywith a set of bolts to annular flange 42, and an annular flange 55, andan outer, tubular conduit 56 spaced from inner conduit 52, betweenannular flanges 54 and 55 and in alignment with outer conduit 44 to forman annular chamber 57. Segment 51 consists of an inner, tubular section58 and an outer, tubular section 59. Inner, tubular conduit 58 isaxially disposed radially relative to the axis of conduit 52, isconnected at a lower end thereof to conduit 52 providing a material flowpassageway 60 communicating with material flow passageway 53 and isprovided with an annular flange 61 at an upper end thereof which ismated and connected to annular flange 26 of lower hopper section 24preferably by a set of bolts. Outer, tubular conduit 59 is spaced frominner conduit 58 and disposed between outer conduit 56 and annularmating flange 61 to form an annular chamber between the inner and outerconduits 58 and 59 communicating with annular chamber 57. Inner conduits52 and 58 also are formed of a gas permeable material and outer conduits56 and 59 are formed of a gas impermeable material. Chamber 57 also isprovided with an inlet connected to a source of fluid under pressure sothat a fluidizing gas may be supplied to chamber 57 and the chamberformed between conduits 58 and 59 to permeate conduits 52 and 59 andthus provide boundary layers consisting of a mixture of fluidizing gasand particles of the bulk material being conveyed. The lower end ofsection 32 further is provided with an inlet conduit 62 which may beconnected to a source of gas under pressure to permit bursts of gas tobe injected axially into section 32, axially relative to segment 51, todislodge any bulk material introduced through segment 51 and settled inpassageway 53 within conduit 52.

As previously indicated, transition section 33 is similar to transitionsection 32 in construction and function. It includes an upper segment 60comparable to segment 50 and a segment 61 comparable to but constructedslightly differently than section 51. Segment 60 is provided with anannular flange 62 which is mated and connected to annular flange 43 toconnect transition section 33 to transport line 30 and an annular flange63 at the opposite end thereof. As best shown in FIG. 4, the outer,impermeable conduit 64 flares downwardly and outwardly and is providedwith a peripheral flange 65 which is connected to peripheral flange 27of receptacle 21. As also shown in FIG. 4, segment 60 includes an inner,permeable conduit 66 providing a material flow passageway 67communicating with material flow passageway 41 and spaced from theouter, impermeable conduit 68 and a permeable, inner conduit 69providing a material flow passageway 70 intercommunicating passageway 67and the opening in flange 65 and spaced from outer impermeable conduit64 to provide a chamber therebetween. As in the previously describedsection, fluidizing air under pressure is supplied to the chamberbetween the inner and outer conduits of section 60 which permeatesthrough the inner conduits thereof to enhance the flow of materialtherethrough.

Mounted on and connected to annular flange 55 is an annular end plate71. Similarly mounted and connected to annular flange 63 is an annularend plate 72 which is similar in construction to end plate 71. Referringto FIGS. 5 and 6, end plate 71 will be seen to include an annular, mainbody portion 73 providing an axial opening 74 and a set ofcircumferentially spaced threaded studs 75. As shown in FIG. 3, abearing 76 is mounted on end plate 74 by means of threaded studs 75 andan end portion of shaft 77 extends through opening 74 of end plate 71and is journaled in bearing 76. The opposite end of shaft 77 similarlyextends through an axial opening in end plate 72 and is journaled in abearing 78 mounted on end plate 72.

Referring to FIG. 2, there also is mounted on the end of end plate 71, asupport bracket 79. Mounted on the support bracket is a drive unit 80including a variable speed, DC motor 81 provided with a gear reductionunit 82 operatively connected to the end of auger shaft 72 extendingthrough the mounting bracket.

In the operation of the assembly shown in FIGS. 1 through 6, bag 25filled with bulk material to be conveyed to receptacle 21 is positionedin a suspended manner on support frame 33 so that the lower end thereofis received in the upper end of hopper 20. Certain controls are thenoperated to supply fluidizing air to the chambers of conveyor 30 betweenthe inner and outer conduits thereof which correspondingly is caused topermeate the inner, permeable conduits thereof. Motor 81 is thenenergized to rotate auger 31. The spout portion of the bag is thenunfolded and freed to permit bulk material in the bag to be gravity fedthrough transition section 32 into the transport line section 30.Material gravity fed into the transport line section is caused to betransported along the length thereof and discharged through transitionsection 33 into receptacle 21 by the action of auger 31. Air permeatingthrough the inner, permeable conduits of conveyor 22 functions toprovide a boundary layer within the permeable conduits consisting of amixture of fluidizing air and particles of the material being conveyed.Such boundary layer not only reduces friction in the flow of materialthrough the conveyor, thus reducing the amount of torque required todrive the auger, but prevents the build up of material in the conveyor.The flow rate of material transported by the conveyor may be adjustedmerely by varying the speed of motor 81. In the event material fed fromthe hopper into the conveyor may settle in transition section 32 tendingto clog or impair the flow of material in the conveyor, a burst of airmay be injected through inlet 62 to dislodge any such buildup ofmaterial. In addition, in lieu of simply an opening between lower hoppersection 24 and transition section 32, an air lock or rotary valve may beprovided therebetween. In the further event that it is desired to cleanthe interior of the conveyor, drive unit 80, support bracket 79 and endplate 71 may be removed from one end of the conveyor and end plate 72may be removed from the other end of the conveyor to permit removal ofthe auger and provide access to the interior of the conveyor. Inaddition, if required, transition sections 32 and 33 may be detachedfrom transport line section 33 for cleaning, maintenance or repairpurposes.

FIGS. 7 through 10 illustrate several systems embodying the presentinvention and incorporating the conveyor as shown in FIGS. 2 through 6,which are operable to convey controlled amounts of bulk materials oftenrequired in various processes and for other purposes. Referring to FIGS.7 and 8, there is illustrated a system 90 including a vessel 91containing a bulk material to be conveyed in metered amounts, a screwconveyor 22 as previously described, a bulk solids mass flowmeter 92, acontroller 93 and a motor control 94. Transition section 33 of the screwconveyor is connected to the lower discharge end of vessel 91 so thatmaterial within the vessel will be gravity fed into the screw conveyor.The screw conveyor transports the material to transition section 32which functions to discharge the material through flowmeter 92 into thedesired receptacle. Controller 93 receives an analog or digital massflow rate output signal from flow meter 92 compares the sensed mass flowrate to a setpoint mass flow rate, and sends a signal to motor controlunit 94 to incrementally either increase or decrease the motor speed tobring the feeder output rate to match the setpoint feed rate. Thisarrangement may be provided with an impact mass flowmeter to determineinstantaneous mass flow and provide a feedback signal to the controllerto close the control loop for motor speed adjustment to meet the desiredflow rate. Such system would use a continuously variable speed drivemotor. The total weight of material discharged could be estimated bynumerical integration of the output signal of the mass flowmeter withrespect to time.

FIG. 9 illustrates a system 100 which includes a vessel 101 containing abulk material to be fed in a metered amount to a receptacle, a screwconveyor 22, a receiving hopper 102, a controller 103 and a motorcontrol 104. Receiving hopper 102 is provided with a slide valve 105 atthe discharge end thereof operated by a solenoid actuator 106, andfurther is provided with a set of load cells 107 for sensing the weightof material deposited in the receiving hopper. In the operation of thesystem, material is gravity from vessel 101 into the screw conveyor 22which transports the material to the receiving hopper 102. The loadcells sense the weight of material fed to the receiving hopper and emita signal to the controller which compares the weight of material addedto the receiving hopper with a setpoint weight within a preset tolerancelimit and sends a control signal to motor control 104 to reduce thespeed thereof thus reducing the discharge rate of the screw conveyor andcorrespondingly reducing the likelihood of overshooting the setpointweight. Upon reaching a second preset weight tolerance limit relative tothe setpoint weight, the controller signals the motor control to stopthe motor. The second preset tolerance usually is made sufficient toaccount for material in transit between the screw conveyor and thereceiving hopper, as well as material which is discharged from the screwconveyor as it continues to operate to a stop.

The gain-in-weight system shown in FIG. 9 measures the net weight of thereceiving hopper to determine how much the feeder has discharged. Suchsystem would most generally be used for batch weighing and notcontinuous metering. The drive motor would be set up with a more or lessfixed high delivery speed rate and a more or less fixed low deliveryspeed rate to slowly approach the setpoint weight of material depositedin the hopper.

System 110 shown in FIG. 10 is comparable to the system shown in FIG. 9and includes a hopper 111 holding a bulk material to be dispensed inmetered amounts, a screw conveyor 22 which is gravity fed material fromhopper 111, a controller 112 and a motor control 113. The dispensinghopper is provided with a set of load cells 114 which function to sensea weight loss of material in hopper 111 and conveyor 22, and transmitsuch data to controller 112. In operation, the signal produced by theload cells is compared to a setpoint weight inputted into thecontroller, within a preset tolerance limit, and the controller sends asignal to the motor controller to reduce the speed of the screwconveyor, making provision for overshooting the setpoint weight. Uponreaching a second preset weight tolerance limit from the set pointweight, the controller signals the motor control to discontinue theoperation of the motor. The second preset tolerance is made sufficientto account for material which is discharged from the screw conveyor asit slows down to a complete stop. This system also may be employed forcontinuous metering applications by calculating the weight of thematerial being discharged from the screw conveyor on a per unit of timebasis and adjusting the speed of the drive motor upwardly or downwardlyuntil the calculated discharge rate is within an acceptable tolerancefrom the desired discharge rate.

In this system, the combined weight of feed hopper 111 and screw feeder22 and their contents is suspended on load cells 114. Thus during normalfeeding any change in system weight measured via the load cells amountsto the weight of material which has been discharged from the outlet ofthe screw conveyor. This system can be operated in a batch mode similarto the gain-in-weight system described previously and using a fixed highspeed and fixed low speed drive arrangement to rapidly approach targetweight then to slowly advance to within a close tolerance of targetweight with allowance of settling of in-flight material.

This system can also act as a continuous metering type system bydifferentiating the change in net weight with respect to time andvarying screw conveyor speed to obtain the desired rate of discharge.When operating in this manner, it is necessary to suspend ratecalculation and hold a fixed screw conveyor speed whenever the feedhopper empties to the point at which it must be refilled to ensurecontinuous product delivery.

In the use of any of the described systems, it will be appreciated thatcontrollable amounts of bulk material may be conveyed from a first siteto a second site for processing or other purposes. In the arrangementutilizing a flow meter to measure the mass flow rate from the screwconveyor, it is possible to operate such system in a batch mode bynumerically integrating the mass flow rate signal from the solid massflowmeter although the accuracy may not be as good as the weight gain orweight loss systems.

Although a single auger profile is illustrated, it further is to beunderstood that augers of different flights may be utilized within thescope of the invention including helicoids, ribbon, cut, cut and folded,fixed or adjustable mixing paddles, non-metallic, hollow, brush andother flights. It further will be appreciated that the screw conveyormay be of a modular construction comprised of a number of componentsthat may be configured as desired, and readily disassembled forcleaning, maintaining or repairing and quickly reassembled and placed inservice. The provision for supplying fluidizing air to the material flowpassageways of the conveyor not only enhances the flow rate of thematerial being conveyed and reduces if not eliminates the deposit ofmaterial but provides for a more precise metering of the material beingconveyed and substantially reduces the torque required to drive theconveyor.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations and modifications of the presentinvention, which come within the province of those persons havingordinary skill in the art to which the aforementioned inventionpertains. However, it is intended that all such variations not departingfrom the spirit of the invention be considered as within the scopethereof as limited solely by the appended claims.

1. A method of transporting metered amounts of a particulate, bulkmaterial, comprising: conveying said material received at an upstreamsite to a downstream site by means of an auger disposed in a conduithaving a body formed of a permeable material, said conduit having amaterial inlet at said upstream site, said conveying material enteringsaid conduit through said inlet, said auger, driven by a motor;supplying a gas under pressure through said body to form a boundarylayer of fluidizing gas along an inner surface of said conduit; sensingthe mass flow rate of said material received at said downstream site;and varying the operation of said motor responsive to differencesbetween said sensed flow rate and a selected flow rate to incrementallyincrease or decrease the speed thereof to achieve said selected flowrate.
 2. A method according to claim 1 including gravity feeding saidmaterial into said conduit.